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    Author(s): David B. South; Curtis L. VanderSchaaf
    Date: 2006
    Source: Gen. Tech. Rep. SRS-92. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. pp. 333-337
    Publication Series: Miscellaneous Publication
    PDF: View PDF  (285 KB)

    Description

    The initial effects of a silvicultural treatment on height or volume growth sometimes decline over time, and the early gains eventually disappear with very long rotations. However, in some reports initial gains are maintained until harvest but due to statistical analyses, a researcher might conclude the treatment effect has "washed-out" by ages 10 to 18 years (even when the gain is 6 green tons per acre or more). This claim is sometimes made even when the volume gains have increased over time. Researchers who end up making Type II statistical errors do so because of the inherent variability which increases with stand age (i.e., statistical power declines over time). To avoid making Type II errors, some researchers have decided to model their data instead of applying statistics to a data set that has low power.

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    Citation

    South, David B.; VanderSchaaf, Curtis L. 2006. The statistical reason why some researchers say some silvicultural treatments "wash-out" over time. Gen. Tech. Rep. SRS-92. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. pp. 333-337

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